The subject of the present invention is semiconductor laser diode laser devices and, in particular, such devices consisting of an array of laser diodes. It also relates to a process for producing such laser devices.
A laser diode device is known, for example from U.S. Pat. No. 5,128,951, which has:
a plurality of parallel and spaced-apart walls, made of a material which is a good heat conductor, which have at least approximately coplanar free longitudinal edges bearing films of an electrically conductive material which extend on each side of said edges on both faces of said walls; PA0 a plurality of semiconductor strips incorporating said laser diodes, each strip comprising an emitting surface via which the laser diodes of the corresponding strip emit, said semiconductor strips being housed longitudinally in the spaces between said walls and each of said semiconductor strips being fastened to the opposite faces of the two walls between which it is housed, so that said semiconductor strips are electrically connected in series by said films of electrically conductive material and so that the emitting surfaces of said semiconductor strips are at least approximately coplanar with said free longitudinal edges of said walls; and PA0 fluid-circulation cooling means intended for cooling said diode strips. PA0 in that said parallel and spaced-apart walls are formed by individual plates joined together, with said semiconductor strips interposed between them as spacers; PA0 in that said semiconductor strips occupy only one longitudinal part of the spaces between plates, in which spaces they are housed; and PA0 in that those longitudinal parts of said spaces between plates which are not occupied by said semiconductor strips serve as circulation channels for said cooling fluid. PA0 a plurality of identical rectangular individual plates made of a material which is a good heat conductor are prepared, at least their two large faces and one of their longitudinal edges are polished and said polished longitudinal edges and the lateral regions contiguous with said polished large faces are covered with films of a material which is a good electrical conductor; PA0 a plurality of identical rectangular semiconductor diode strips, one longitudinal edge of which serves as an emitting surface to said diodes and the two large faces of which are covered with electrically conductive contact films, are prepared; PA0 the contact films of said strips are applied against the lateral regions of the films of electrically conductive material of said plates, between which are interposed electrically conductive fastening films; and PA0 said plates and said strips are fastened together through the action of said fastening films, with application of pressure. PA0 a stack of all said plates and all said strips is produced so that: PA0 the entire said stack is raised to a temperature corresponding to the melting point of said solder films, while at the same time subjecting said stack to pressure transversely with respect to said plates and strips, after which said stack is left to cool. PA0 during the preparation of said plates, one of said lateral films of conductive material of each plate is covered with a film of a first electrically conductive solder; PA0 a plurality of subassemblies, each of which comprises a plate and a strip, are formed by superposing, each time, a plate and a strip so that the solder film of the plate is superposed with a contact film of the strip and so that the longitudinal edge of said plate is at least approximately coplanar with the emitting surface of the strip, then by raising each subassembly to a temperature corresponding to the melting point of said first solder while at the same time subjecting it to pressure transversely with respect to said plate and to said strip, after which said subassembly is left to cool; PA0 in each subassembly, the other of said lateral films of conductive material of the corresponding plate is covered with a film of a second electrically conductive solder having a melting point below that of said first solder; PA0 a stack of said subassemblies is formed by superposing them, each time so that the other contact film of the strip of one subassembly is applied against the film of said second solder of the plate of another subassembly and so that the longitudinal edges of all the plates are at least approximately coplanar with each other and with the emitting surfaces of said strips; and PA0 said stack of subassemblies is raised to a temperature corresponding to the melting point of said second solder, while at the same time subjecting said stack to pressure transversely with respect to said plates and strips, after which said stack of subassemblies is left to cool.
The known laser devices of this type include a block of material which is a good heat conductor, which is supported by said fluid-circulation cooling means. Parallel grooves are machined, mechanically or chemically, in said block, said grooves forming the housings for said diode strips and defining ribs between them, each of these ribs forming one of said walls to which said diode strips are soldered. On the opposite side from the free longitudinal edges of the ribs, the latter are joined together by a base which corresponds to that part of said block which is not cut into by said grooves and via which said block is connected to said cooling means.
Such known laser devices have many drawbacks.
First of all, the removal of the heat generated by said diodes is not good. This is because, between the diode strips and the cooling fluid, the heat must travel a long path which passes through the soldered joints between the strips and the ribs, along the height of said ribs, through said base and, finally, through the wall of said cooling means which supports said base. Moreover, in order to be able to house said strips in said grooves easily, it is absolutely essential to provide clearances which are compensated for by the solder. Consequently, the soldered joints between the diode strips and the grooves are thicker than would be sufficient to ensure electrical contact, so that the rate of heat transfer is reduced at said soldered joints. This heat transfer rate reduction effect is increased because of the fact that the planarity and rugosity of the side walls of the ribs cannot be optimized when cutting out said grooves. These known laser devices therefore cannot provide a high radiation density because the heat removal is insufficient. If a high radiation density is desired, the laser diodes therefore overheat and are rapidly destroyed.
Moreover, because of the necessary existence of clearances between the diode strips and the ribs and the impossibility of applying satisfactory pressure between said strips and said ribs during soldering, the continuity of the electrical contact between said diode strips may be defective, despite--or because of--the relatively large thickness of said soldered joints.
Furthermore, the machining of said grooves and the fitting and soldering of said strips in them require a very high precision, not very compatible with industrial manufacture and reasonable manufacturing costs.